Amperometric analyzer



Se t. 8, 1953 J. F. HALLER AMPEROMETRI C ANALYZER Filed Feb. 4. 194811/2167 JoZuZzfozz ATTORNEYS Patented Sept. 8, 1953 AMPERbMETRICANALYZER is i J ohnF. Hallen Niagara Falls, N.- Y., assignor toMathleson Chemical Corporation, a corporation of Virginia 7 ApplicationFebruary 4, 1948, Serial No. 6,189

3 Claims. (Cl. 204-195) My invention concerns amperometry and moreparticularly pertains to 'an amperometric-device suitable fordetermining -the concentration of an oxidizing or reducinggas in agaseous mixture comprising such a gas. The device is especially valuableas applied in the analysis of gas-mix.- tures containing chlorine eitheras such or in the form of chlorine dioxide. 7

The need has long existed for a device of the character indicated whichis suitable forcontinuous operation and which can be adapted to providecontinuous automatic indication and recording. Whilemany amperometricdevices have been proposed for use in the analysis of aqueous solutionsof oxidizing gases, chlorine water, for example, these in the mainaregrossly inaccurate when applied in the analysis of gaseous mixture.

The device herein is of simple construction and, accordingly, can beproduced in quantity and at a reasonable cost. Although it willdoubtless be considered a valuable laboratory tool, I consider itchiefly significant as a means of process control. ThusQit may beapplied in the manufacture of chlorine dioxide, as by generation fromacidified chlorate solutions with reducing gases,

to insure safedilution of the product gas with inert gas. An interestingand related application of the device is disclosed in the copendingpatent application of Gordon D. Byrkit, Serial No.

787,573, filed November 22, 1947 (now abandoned), which describes andclaims av novel method of air-conditioning and a novel system ofair-conditioning apparatus. The device is also highly useful as aWarning device in the manufacture of hydrazine, for example bythe'meth'od described in copending application Serial No. 784,809,filed, November 8, 1947; 'It may be placed in strategic positions in theplant and through a relay may actuate a suitable signal when theconcentration of hydrazine in the air exceeds a critical value. Sulfurdioxide and nitrogen peroxide are exemplary of gases other than chlorinewhich may be detected or measured with the device.

I shall describe my invention with the aid of the accompanying drawing,a sectional elevation, illustrating a preferred embodiment thereof.

In the drawing, numeral denotes a tube constructed of a material, asglass, impermeable with respect to an electrolyte solution II, which maybe a saturated solution of sodium or potassium chloride, for example.Tube l l is closed at its upper end by a stopper l 2, a rubber stopperbeing normally used. Tubular section H, which with the tube It) forms areceptacle for the reservoir of electrolyte solution, is constructed ofa material, as porous clay, permeable with respect to the solution. I

A silver electrode 15 is immersed in the electrolyte solution, while aplatinum wire electrode I6 is wound about the porous tubular section l4.Terminals l1 and 18 are provided for con necting leads [9 and 20,respectively, the circuit being completed through a microammeter' 2|.

The latter is illustrated diagrammatically since, of itself. it forms nopart of the invention herein. The different potentials between theelectrodes and their respective solutions causes a current to flowtherebetween without the nec'essity of impressing an external source ofcurrent.

Although, as indicated,'I prefer silver as the reference electrode, agold, lead or graphite electrode may be used with a suitableelectrolyte. Lithium sulfate solution, saturated at room tem: perature,is recommended with a lead electrode. Less costly metals than platinum,nickel, for "example, may be used for the external electrode when it isknown that the metal is not deleteriously' afiected by any of'the gaseswith which it. will come into contact. The external electrode must havethe form of a wire rather than aribbon, i. e. it should be substantiallyround or at least elliptical in cross section and it must be so woundabout the porous surface that there isno contact between individualcoils. For best results the diameter of the wire should notsubstantially exceed 0.05 inch. In the preferred construction the wirehas a diameter of from .003 to .02 inch and is so wound that the spacingbetween the coils is substantially uniform.

In use, the device is enclosed within a gastight chamber, not shown,into which is led the gas mixture containing the gas, the concentrationof which it is desired todetermine. The electrolyte solution bleeds.through the porous tubular section with the result that a film ofsolution is at all times maintained on the outside of the porous sectionin contact with the platinum electrode. When the gas mixture comes intocontact with the film of electrolyte, the oxidizing or reducing gasdissolves reversibly therein and an equilibrium concentration is quicklyestablished which determines the current through the microammeter.

It may be considered desirable in some applications to conserveelectrolyte solutionby using a porous tubular section having a porositysomewhat less than that indicated. In such case, if

r the rate of flow of solution through the porous ride and because itssolubility changes little,

with changing temperatures. Other salts may, however, be used, either inthe form of saturated solutions or solutionsof lesser concentration. Itis only necessary that the electrolyte does not chemically attack eitherof the electrodes and that the negative ions of the electrolyte form aslightly soluble salt with the internal reference electrode. Generally,preferred with a silver or mercury electrode, sulfates with a leadelectrode; In some cases aqueous solutions of acids or alkalies may beused as the electrolyte.

. Variations in temperature have little effect on the operation of thedevice and may be permitted provided proper precautions are taken .tomaintain constant electrolyte concentration.

Using the preferred sodium chloride, a constant concentration of theelectrolyte in contact with the reference electrode is most convenientlymaintained at room temperature.

a When external washing of the electrode is necessary I generallyutilize an aqueous solution of a buffering electrolyte, e. g. sodiumbicarbonate in an effective concentration, usually 2-l0%. In theapplication of my device to the detection of hydrazine vapors in thepresence of ammonia, it is desirable to washthe. electrode externallywith a 2-10% solution of sodium hydroxide. This prevents the solution ofammonia but does not interfere with the effect of hydrazine in causing'acurrent to flow through the circuit.

Example I The device shown in the drawing was suspended in a 2-literbeaker of air. The inner electrode was silver, the outer platinum. Theinner electrode was supplied with sodium chloride solution saturated atroom temperature.

The contents of a 400. ml. beaker containing a chlorine dioxide-airmixture of about 35 mm. partial pressure of the former was partiallydecantedinto the larger beaker. The ammeter promptly showed a current of15 microamperes.

Example II After flushing the 2-liter beaker used in Example I with aflow of air, 100 ml. of chlorine water freshly prepared at 18 C. waspoured into the bottom of the beaker. The ammeter indicated increasingamounts of chlorine in the gaseousphase in which the electrode wassuspended, up to a maximum of 18 microamperes.

chlorides are.

Example III The electrode was suspended in air in a clean 2-liter beakerand supplied as before with saturated sodium chloride solution. Theelectrode was also externally washed by dropping thereon continuously a5% sodium hydroxide solution. The vapors from a bottle of. 98% hydrazinehydrate were decanted: into the beaker and a current of 20 microampereswas indicated.

In each of the foregoing examples, before my analyzer was exposed to anatmosphere containing oxidizing vapors, but after the sodium chloride,electrolyte solution had been added, the instrument was. allowed to cometo equilibrium in air, as, indicated by a low constant reading of themicroammeter. When such equilibrium was obtained, the indicating needlewas re-set to give a zero reading.

I claim:

1. An instrument fordetecting and measuring concentrations of oxidizingand reducing gases in gaseous mixtures which comprises an elongatedhollow receptacle confining a reservoir of electrolyte, a transverseportion of which hollow receptacle is permeable with respect to theelectrolyte, an electrode disposed within the hollow receptacle spacedfrom the inner walls thereof extending within the permeable portion ofthe receptacle and surrounded by the reservoir of electrolyte, a secondelectrode having the form of a wire wound in spaced turns about theouter surface of the permeable portion of the receptacle, and an ammeterdirectly connected between the two electrodes completing an electricalcircuit through the electrodes and elec- 'trolyte having no externalsource of electrical energy.

2. An instrument according to claim 1 in which the elongated hollowreceptacle is tubular, the electrode within the receptacle is a silverelectrode, and the second electrode is platinum wire v having a diameternot exceeding .05 inch.

3. An instrument according to claim 1 in which the elongated hollowreceptacle is tubular, theelectrolyte is sodium chloride solution, theelectrode within the receptacle is a silver electrode, and the secondelectrode is platinum wire having a diameter between about .003 and .02inch.

JOHN F. HALLER.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,278,248 Darrah Mar. 31, 1942 2,464,087 Jacobson Mar. 8, 1949OTHER REFERENCES

1. AN INSTRUMENT FOR DETECTING AND MEASURING CONCENTRATIONS OF OXIDIZINGAND REDUCING GASES IN GASEOUS MIXTURES WHICH COMPRISES AN ELONGATEDHOLLOW RECEPTACLE CONFINING A RESERVIOR OF ELECTROLYTE, A TRANSVERSEPORTION OF WHICH HOLLOW RECEPTACLE IS PERMEABLE WITH RESPECT TO THEELECTROLYTE, AN ELECTRODE DISPOSED WITHIN THE HOLLOW RECEPTACLE SPACEDFROM THE INNER WALLS THEREOF EXTENDING WITHIN THE PERMEABLE PORTION OFTHE RECEPTACLE AND SURROUNDING BY THE RESERVOIR OF ELECTROLYTE, A SECONDELECTRODE HAVING THE FROM OF A WIRE WOUND IN SPACED TURNS ABOUT THEOUTER SURFACE OF THE PERMEABLE PORTION OF THE RECEPTACLE, AND AN AMMETERDIRECTLY CONNECTED BETWEEN THE TWO ELECTRODES COMPLETING AN ELECTRICALCIRCUIT THROUGH THE ELECTRODE AND ELECTROLYTE HAVING NO EXTERNAL SOURCEOF ELECTRICALLY ENERGY.